This invention relates to scan conversion apparatus for converting scan data sensed in non-raster format to a raster scan format for display on a conventional cathode ray tube (television monitor). More particularly, the invention relates to a peak detecting digital scan converter for an ultrasonic multi-sector scanner for storing and reading out for display only the largest amplitude echo data for image points covered by overlapping sector scans.
The multi-sector scanner or "walking beam" ultrasonic imaging system has been suggested as a way to improve the quality of ultrasound echo images. This real time imaging system has a linear transducer array as depicted in FIG. 1 for producing a set of sector scans with the origin points of the sequential sector scans displaced longitudinally along the array. For each sector scan a sub-array of transducer elements are excited in time sequence to generate angulated acoustic beams at many different angles relative to the normal at the midpoint of the sub-array. Directional pulses of ultrasound impinge upon the object of interest at varying angles, and the system is characterized by an increase in the range of total viewing angles which improves reception of specular reflections. This ultrasonic scanning system is described in concurrently filed application Ser. No. 825,528 by H. A. F. Rocha and C. E. Thomas, entitled "Ultrasonic Multi-Sector Scanner", and assigned to the assignee of this invention.
Because insonification of interior objects takes place at varying angles, any given point of the object can produce echoes from many different acoustic beams. To store and display all these echoes at the same pixel (picture element) of a cathode ray tube display device would improperly enhance or perhaps partially white-out overlapping areas of the field of view. Therefore, it has been suggested that the image be displayed using an analog storage tube or scan converter tube operated in a "peak detection" mode, in which the largest signal to be written on the target is the signal finally stored on the target. In this mode of operation, no accumulatin of charge takes place over and above that needed to reflect the largest signal written onto a given part of the target. However, analog storage tubes are sensitive, difficult to align, nonuniform and nonlinear.